1. Field of the Invention
The present invention relates to a power supply switching circuit.
2. Description of the Related Art
A conventional power supply switching circuit is described. FIG. 4 is a circuit diagram illustrating the conventional power supply switching circuit.
A detector 31 compares a voltage VCC and a voltage VBK and controls a selection circuit 33 based on a result of the comparison. Based on the result of the comparison, the selection circuit 33 selects higher one of the voltage VCC and the voltage VBK and supplies the selected voltage to the detector 31, a detector 32, and a switching circuit 34 as a voltage VCH.
The detector 32 compares the voltage VCC and a detection voltage VDET and controls the switching circuit 34 based on a result of the comparison. Specifically, if the voltage VCC is higher than the detection voltage VDET, the detector 32 outputs an output voltage of High level, and then the switching circuit 34 outputs the voltage VCC to respective output terminals of the detectors 31 and 32 and the power supply switching circuit as a voltage VOUT. If the voltage VCC is lower than the detection voltage VDET, on the other hand, the detector 32 outputs an output voltage of Low level, and then the switching circuit 34 outputs the voltage VBK to the respective output terminals of the detectors 31 and 32 and the power supply switching circuit as the voltage VOUT (see, for example, Japanese Patent Application Laid-open No. 2008-086100).
The conventional technology, however, uses the two detectors 31 and 32, and therefore the circuit scale of the power supply switching circuit increases.